[PATCH 4/4] drm/i915/uapi: convert i915_query and friend to kernel doc

[Jason Ekstrand]

Reviewed-by: Jason Ekstrand <jason at jlekstrand.net>

On April 16, 2021 05:37:55 Matthew Auld <matthew.auld at intel.com> wrote:

> Add a note about the two-step process.
>
> v2(Tvrtko):
>  - Also document the other method of just passing in a buffer which is
>    large enough, which avoids two ioctl calls. Can make sense for
>    smaller query items.
>
> Suggested-by: Daniel Vetter <daniel at ffwll.ch>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Kenneth Graunke <kenneth at whitecape.org>
> Cc: Jason Ekstrand <jason at jlekstrand.net>
> Cc: Dave Airlie <airlied at gmail.com>
> Cc: dri-devel at lists.freedesktop.org
> Cc: mesa-dev at lists.freedesktop.org
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
> include/uapi/drm/i915_drm.h | 61 ++++++++++++++++++++++++++++++-------
> 1 file changed, 50 insertions(+), 11 deletions(-)
>
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index d79b51c12ff2..12f375c52317 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -2218,14 +2218,23 @@ struct drm_i915_perf_oa_config {
> 	__u64 flex_regs_ptr;
> };
>
> +/**
> + * struct drm_i915_query_item - An individual query for the kernel to process.
> + *
> + * The behaviour is determined by the @query_id. Note that exactly what
> + * @data_ptr is also depends on the specific @query_id.
> + */
> struct drm_i915_query_item {
> +	/** @query_id: The id for this query */
> 	__u64 query_id;
> #define DRM_I915_QUERY_TOPOLOGY_INFO    1
> #define DRM_I915_QUERY_ENGINE_INFO	2
> #define DRM_I915_QUERY_PERF_CONFIG      3
> /* Must be kept compact -- no holes and well documented */
>
> -	/*
> +	/**
> +	 * @length:
> +	 *
> 	 * When set to zero by userspace, this is filled with the size of the
> 	 * data to be written at the data_ptr pointer. The kernel sets this
> 	 * value to a negative value to signal an error on a particular query
> @@ -2233,21 +2242,26 @@ struct drm_i915_query_item {
> 	 */
> 	__s32 length;
>
> -	/*
> +	/**
> +	 * @flags:
> +	 *
> 	 * When query_id == DRM_I915_QUERY_TOPOLOGY_INFO, must be 0.
> 	 *
> 	 * When query_id == DRM_I915_QUERY_PERF_CONFIG, must be one of the
> -	 * following :
> -	 *         - DRM_I915_QUERY_PERF_CONFIG_LIST
> -	 *         - DRM_I915_QUERY_PERF_CONFIG_DATA_FOR_UUID
> -	 *         - DRM_I915_QUERY_PERF_CONFIG_FOR_UUID
> +	 * following:
> +	 *
> +	 *	- DRM_I915_QUERY_PERF_CONFIG_LIST
> +	 *      - DRM_I915_QUERY_PERF_CONFIG_DATA_FOR_UUID
> +	 *      - DRM_I915_QUERY_PERF_CONFIG_FOR_UUID
> 	 */
> 	__u32 flags;
> #define DRM_I915_QUERY_PERF_CONFIG_LIST          1
> #define DRM_I915_QUERY_PERF_CONFIG_DATA_FOR_UUID 2
> #define DRM_I915_QUERY_PERF_CONFIG_DATA_FOR_ID   3
>
> -	/*
> +	/**
> +	 * @data_ptr:
> +	 *
> 	 * Data will be written at the location pointed by data_ptr when the
> 	 * value of length matches the length of the data to be written by the
> 	 * kernel.
> @@ -2255,16 +2269,41 @@ struct drm_i915_query_item {
> 	__u64 data_ptr;
> };
>
> +/**
> + * struct drm_i915_query - Supply an array of drm_i915_query_item for the 
> kernel
> + * to fill out.
> + *
> + * Note that this is generally a two step process for each drm_i915_query_item
> + * in the array:
> + *
> + * 1. Call the DRM_IOCTL_I915_QUERY, giving it our array of 
> drm_i915_query_item,
> + *    with drm_i915_query_item.size set to zero. The kernel will then fill in
> + *    the size, in bytes, which tells userspace how memory it needs to 
> allocate
> + *    for the blob(say for an array of properties).
> + *
> + * 2. Next we call DRM_IOCTL_I915_QUERY again, this time with the
> + *    drm_i915_query_item.data_ptr equal to our newly allocated blob. Note 
> that
> + *    the i915_query_item.size should still be the same as what the kernel
> + *    previously set. At this point the kernel can fill in the blob.
> + *
> + * Note that for some query items it can make sense for userspace to just pass
> + * in a buffer/blob equal to or larger than the required size. In this 
> case only
> + * a single ioctl call is needed. For some smaller query items this can work
> + * quite well.
> + *
> + */
> struct drm_i915_query {
> +	/** @num_items: The number of elements in the @items_ptr array */
> 	__u32 num_items;
>
> -	/*
> -	 * Unused for now. Must be cleared to zero.
> +	/**
> +	 * @flags: Unused for now. Must be cleared to zero.
> 	 */
> 	__u32 flags;
>
> -	/*
> -	 * This points to an array of num_items drm_i915_query_item structures.
> +	/**
> +	 * @items_ptr: This points to an array of num_items drm_i915_query_item
> +	 * structures.
> 	 */
> 	__u64 items_ptr;
> };
> --
> 2.26.3

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